Knife sharpener



FIG. 1 is a top front right isometric view of a knife sharpener in accordance with the present design;

FIG. 2 is a bottom left isometric view thereof;

FIG. 3 is a front view thereof;

FIG. 4 is a rear view thereof;

FIG. 5 is a left view thereof;

FIG. 6 is a right view thereof;

FIG. 7 is a top view thereof; and,

FIG. 8 is a bottom view thereof.

The broken lines depict portions of the article that form no part of the claimed design. 

CLAIM The ornamental design for a knife sharpener, as shown and described. 